The "Mission Accomplished" boast has been mocked many times since Mr. Bush's carrier speech as criticism has mounted over the failed search for weapons of mass destruction and the continuing violence in Iraq.
When it was brought up again Tuesday at a news conference, Mr. Bush said, "The 'Mission Accomplished' sign, of course, was put up by the members of the USS Abraham Lincoln, saying that their mission was accomplished."
"I know it was attributed somehow to some ingenious advance man from my staff — they weren't that ingenious, by the way."
That explanation hadn't surfaced during months of questions to White House officials about proclaiming the mission in Iraq successful while violence continued.
After the news conference, a White House spokeswoman said the Lincoln's crew asked the White House to have the sign made. The White House asked a private vendor to produce the sign, and the crew put it up, said the spokeswoman. She said she did not know who paid for the sign.
Later, a Pentagon spokesman called The Associated Press to reiterate that the banner was the crew's idea.
"It truly did signify a mission accomplished for the crew," Navy Cmdr. Conrad Chun said, adding the president's visit marked the end of the ship's 10-month international deployment.
The president's appearance on the Abraham Lincoln, which was returning home after service in the Persian Gulf, included his dramatic and much-publicized landing on the ship's deck.
Mr. Bush's disavowal Tuesday brought new criticism from at least three of the Democrats seeking their party's nomination to run against the president — John Kerry, Wesley Clark and Joe Lieberman.
"Today was another banner day in George Bush's quest to bring honor and integrity to the White House," Lieberman said. "If he wanted to prove he has trouble leveling with the American people, mission accomplished."
Since Mr. Bush declared an end to major combat in Iraq on May 1, 115 U.S. soldiers have been killed by hostile fire — more than died in combat before the speech.
In his Rose Garden press conference, Mr. Bush told the reporter who asked about the sign: "I think you ought to look at my speech. I said, Iraq is a dangerous place and we've still got hard work to do, there's still more to be done. And we had just come off a very successful military operation. I was there to thank the troops."
The president said his statement "was a clear statement, basically recognizing that this phase of the war for Iraq was over and there was a lot of dangerous work. And it's proved to be right, it is dangerous in Iraq."
In the May 1 speech, Mr. Bush did note that the job in Iraq was not complete, promising "difficult work" in Iraq "bringing order to parts of that country that remain dangerous," he said.
Later he added: "The transition from dictatorship to democracy will take time, but it is worth every effort. Our coalition will stay until our work is done."
But Mr. Bush also sounded a triumphant note, describing the Iraqi operation as a "victory in a war on terror."
"In the battle of Iraq, the United States and our allies have prevailed," he said. "And now our coalition is engaged in securing and reconstructing that country."
The president's USS Lincoln speech came under scrutiny almost immediately. Democrats claimed the White House wasted taxpayer dollars and sailors' time on a publicity stunt.
Despite initial claims that the ship was too far out to sea for a helicopter landing, forcing the president to use a jet, the Lincoln was actually within helicopter range when Mr. Bush arrived.
The jet flight was much more dramatic than a helicopter arrival would have been, as the president took the control stick for part of the flight and emerged on deck wearing a flight suit and helmet.
In addition, Pentagon officials told the Washington Post that after the president's speech, the Lincoln waited offshore for hours while he slept rather than heading into port after its 10-month voyage.